Manual braking system with hydraulic brake booster

ABSTRACT

A hydraulic pressure intensifier for operating a vehicle braking system under conditions that are not conducive to the proper operation of a power assist for the braking system. The hydraulic pressure intensifier has an intensifier inlet fluidly connected to a master cylinder and an intensifier outlet fluidly connected to a wheel cylinder. A bypass valve has an input and output fluidly connected to the intensifier inlet and the intensifier outlet, respectively. With normal power assisted braking operation, the bypass valve is open and the master cylinder is fluidly connected to the wheel cylinder via the bypass valve. In a manual or nonpower assisted braking operation, the bypass valve is closed; and the hydraulic pressure intensifier is fluidly connected between the master cylinder and the wheel cylinder. Thus, with the bypass valve closed, a fluid pressure from the master cylinder that is applied to the inlet of the intensifier cylinder is multiplied to a greater fluid pressure at the outlet of the intensifier cylinder and applied to the wheel cylinder.

FIELD OF THE INVENTION

This invention relates to vehicle braking systems and more particularly,to an improved manual-braking mode.

BACKGROUND OF THE INVENTION

There is a continuing effort to improve the performance of vehiclebraking systems in both the powered and unpowered mode. Power or powerassisted braking often uses a fluid pressure actuator such as a vacuumbooster to boost the driver-exerted force on the brake pedal. Such aknown power braking system 18 is schematically illustrated in FIG. 2.Depressing a brake pedal 20 moves a pushrod 22 to the right asillustrated in FIG. 2. The pushrod is connected to a piston rod (notshown) in a master cylinder 24 in a known manner. The pushrod 22 extendsthrough a vacuum booster 26 that contains a diaphragm 28 mechanicallyconnected to the pushrod 22. The diaphragm 28 separates and seals aforward fluid chamber 36 from a rear fluid chamber 38. The forward fluidchamber 36 is connected to the vehicle vacuum system 30, and the rearfluid chamber 38 is vented to atmosphere via a port 32. As the operatorpushes the brake pedal 20, the pushrod 22 operates a control valve (notshown) in a known manner to open the forward chamber 36 to the vacuumsystem 30. Thus, atmospheric pressure in the rearward chamber 38 appliesa substantial force on the diaphragm 28, which translates with thepushrod 22. Thus, the vacuum booster 26 provides a substantial additiveforce to the force supplied by the operator on the brake pedal 20.

Known master cylinders 24 have primary and secondary cylinder portionsthat are operated simultaneously and in parallel in response to thetranslation of the pushrod 22. Therefore, the master cylinder 24provides two independently operable fluid pressure outlets 40, 42.Hydraulic fluid from the first output is fluidly connected to a firstpair of the wheel cylinders 44, 46, and hydraulic fluid from the secondmaster cylinder output 42 is fluidly connected to a second pair of thewheel cylinders 48, 50. On trucks, one of the master cylinder outputs isoften connected to the two front wheel cylinders, and the other mastercylinder output is connected to the two rear wheel cylinders. Onautomobiles, each of the master cylinder outputs is normally connectedto one of the front wheel cylinders and one of the rear wheel cylinders.

For proper braking operation, the master cylinder 24 must displace avolume of hydraulic fluid from each of its outputs 40, 42 that issufficient to properly operate two of the wheel cylinders. Further, thathydraulic fluid displacement and the resulting braking force must beapplied so that the vehicle is stopped in a desired distance. In oneexample, over a typical range of vehicle operation, it is necessary thata range of braking forces, for example, about 2000-8000 pounds, beprovided by the wheel cylinders 44-50. In the absence of the vacuumbooster 26, the mechanical and hydraulic systems within the brakingsystem 18 cause the wheel cylinders 44-50 provide a braking force ofabout 1000 psi. Thus, the vacuum booster 26 is effective to provide anadditional braking system pressure, so that the wheel cylinders 44-50are able to supply the necessary braking forces.

While the engine is running, the vacuum system 30 generates a sufficientvacuum to provide the required power assisted braking. However, as willbe appreciated, if for some reason the vacuum system 30 or vacuumbooster 26 unexpectedly fail or an operator attempts to apply the brakeswithout the engine running, the braking system 18 loses a substantialportion of the available braking force. In the example above, when thevacuum power assist is lost, the braking system loses about 75% of itsbraking force. In that situation, with a limited braking force, theoperator has a very difficult time bringing the vehicle to a stop withina reasonable stopping distance. Thus, there is a continuing effort toimprove the braking capability of the braking system 18 in amanual-braking mode, that is, a braking mode having no power assist fromthe engine.

Consequently, there is a need for an improved braking system that canoperate in a manual or nonpowered mode and be able to provide asubstantially greater braking force than known systems.

SUMMARY OF THE INVENTION

The present invention provides a vehicle braking system having animproved vehicle braking capability when a braking power assist or boostis inoperative, which may occur either when the vehicle engine is off,or there is a failure in the power boost system, or the vehicle engineis not operating normally. Under such conditions, the vehicle brakingsystem of the present invention provides a substantially greater brakingforce in response to a force applied by an operator on a brake pedal.Thus, the vehicle braking system of the present invention substantiallyimproves the operator's capability of stopping the vehicle in a shortertime and over a shorter distance under nonpower assist conditions.

According to the principles of the present invention and in accordancewith the preferred embodiments, the invention provides an apparatus foruse with a vehicle braking system having a brake pedal adapted to beused by an operator. A pushrod has one end connected to the brake pedaland an opposite end connected to a master cylinder. A hydraulic pressureintensifier has an intensifier inlet fluidly connected to the mastercylinder and an intensifier outlet fluidly connected to a wheelcylinder. A bypass valve has an input and output fluidly connected tothe intensifier inlet and the intensifier outlet, respectively. Thebypass valve has an open state that fluidly connects the master cylinderto the wheel cylinder via the bypass valve, and a closed state thatfluidly connects the hydraulic pressure intensifier between the mastercylinder and the wheel cylinder. Thus, a fluid pressure from the mastercylinder that is applied to the inlet of the intensifier cylinder ismultiplied to a greater fluid pressure at the outlet of the intensifiercylinder and applied to the wheel cylinder.

In one aspect of the invention, the hydraulic pressure intensifierincludes an intensifier cylinder with a larger cross-sectional areaadjacent the intensifier inlet and a smaller cross-sectional areaadjacent the intensifier outlet, and an intensifier piston having alarger cross-sectional area disposed in the larger cross-sectional areaof the intensifier cylinder and a smaller cross-sectional area disposedin the smaller cross-sectional area of the intensifier cylinder.

In another aspect of the invention, hydraulic pressure intensifierincludes a bypass valve actuator that may be implemented with a pressuresensor fluidly connected to a vacuum system. The pressure sensorprovides an output signal having a first signal state in response to alower pressure in the vacuum system for opening the bypass valve and asecond signal state in response to a higher pressure in the vacuumsystem for closing the bypass valve.

In another embodiment of the invention, a method is provided foroperating a vehicle braking system with a power assist with the abovedescribed pressure intensifier.

These and other objects and advantages of the present invention willbecome more readily apparent during the following detailed descriptiontaken in conjunction with the drawings herein.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a schematic block diagram of a vehicle braking circuit thatincludes a hydraulic brake booster for use in the manual mode inaccordance with the principles of the present invention.

FIG. 1B is a cross-sectional view of the hydraulic intensifier of FIG. 1showing its operation during a manual-braking mode.

FIG. 2 is a schematic block diagram of a known vehicle braking circuit.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIG. 1, a hydraulic brake booster 60 is inserted in thevehicle braking system 18 between one of the fluid outputs, for example,fluid output 40, of the master cylinder 24 and fluid wheel cylinders 44,46. The hydraulic brake booster 60 is comprised of a bypass valveactuator 62, for example, a pressure or vacuum sensor, a hydraulicbypass valve 64 and a hydraulic pressure intensifier 66. The pressuresensor 62 is fluidly connected to the vacuum system 30 and provides anoutput 63 that is operatively connected to the bypass valve 64. Thebypass valve 64 which may be, for example, an electrically operatedsolenoid valve, is switched between its open and closed states bychanges in state of the signal on the output 63 of the pressure sensor.The bypass valve 64 has a fluid input 65 fluidly connected to the fluidoutput 40 of the master cylinder 24 and a fluid output 67 fluidlyconnected to the wheel cylinders 44, 46.

The hydraulic intensifier 66 is comprised of an intensifier cylinder 68having a stepped bore 70 comprised of a first, larger bore 72 and asecond, smaller bore 74. The first bore 72 has a cross-sectional areathat is larger than the cross-sectional area of the second bore 74. Astepped piston 75 is slidably disposed within the stepped bore 70. Thestepped piston 75 has an integral first, larger piston 76 that isslightly smaller than the first, larger bore 72 of the cylinder 68. Thestep piston 75 has an integral second smaller piston 78 that is slightlysmaller than the smaller bore 74. A larger O-ring 80 provides ahydraulic fluid seal between the larger piston 76 and the larger bore72. A smaller O-ring 82 provides a hydraulic fluid seal between thesmaller piston 78 and the smaller bore 74.

After the stepped piston 75 has been disposed in the cylinder 68, a cap84 is mounted over one end of the cylinder 68. The cap 84 is attached tothe cylinder 68 by threads, adhesives, welding or other known means. AnO-ring 86 is disposed between the cap 84 and the cylinder 68 to preventhydraulic fluid from leaking therebetween. An O-ring 88 is disposed inan interior surface 90 of the cap 84. The O-ring 88 bounds a smallerarea 89 a on a larger, upper, end surface 89 of the stepped piston 75that is about the same as the cross-sectional area of the smaller bore74. It should be noted that hydraulic fluid pressure within the smallerbore 74 is determined not only by an end surface 102 of the smaller end78 of the piston 75 but also by an annular area of O-ring 82 that isbetween the outer circumference of the piston smaller end 78 and thecircumference of the smaller bore 74.

A biasing element 71, for example, a compression spring, biases orforces the stepped piston 75 against the O-ring 88. The hydraulicintensifier 66 has an annular chamber 96 between a cylindrical sidewall91 of the smaller piston 78 and the larger bore 72. The annular chamber96 is vented to atmosphere through vent hole 98. Therefore, the steppedpiston 75 is not subjected to any axial pressure forces from within thechamber 96. Further, since the area within the O-ring 88 is about equalto the cross-sectional area of the smaller piston 78, and in thepower-brake mode with the bypass valve 64 open, the hydraulic pressuresat the fluid inlet 92 and outlet 94 of the hydraulic intensifier 66 areabout equal. Consequently, there is little or no hydraulic fluidpressure differential across the stepped piston 75. Therefore, duringthe power-brake mode, the biasing element 71 is operative to bias theupper surface 89 of the stepped piston 75 firmly biased against theO-ring 88 to create a hydraulic fluid seal therewith.

The hydraulic intensifier 68 has a fluid inlet 92 that is fluidlycoupled to the fluid output 40 of the master cylinder 24. In addition,the hydraulic intensifier 66 has a fluid outlet 94 that is fluidlyconnected to fluid inputs of the wheel cylinders 44, 46 that are alsocommonly connected to a fluid output 67 of the bypass valve 64.

In use, the hydraulic brake booster 60 functions to provide a brakeboosting force when the vehicle braking system 18 is operating in anonpowered or manual mode. Therefore, the hydraulic brake booster 60 isinoperative when the vehicle engine is running and the vacuum booster 26is providing a boost power-brake force. The pressure sensor 62 isfluidly connected to the vacuum system 30 and provides an output thatswitches between two states. The pressure sensor has a first state inresponse to detecting a lower, engine operating vacuum pressure withinthe vacuum system 30 that is provided by a normal engine operation. Ifthe vacuum system fails, for example, through leakage, or the engine isturned off, the pressure within the vacuum system 30 rises. The pressuresensor 62 senses the higher pressure and switches to a second state.

The bypass valve 64 is switched to its open state in response to a firststate of the pressure sensor 62. In other words, when the engine isoperating normally and the pressure sensor detects a lower engineoperating vacuum pressure, the bypass valve 64 is open and provides abypass hydraulic fluid path around the hydraulic intensifier 66. Withthe bypass valve 64 open, the master cylinder 24 has a direct fluidconnection to the wheel cylinders 44, 46. Thus, when the vehicle brakingsystem 18 is operating in the power-braking mode, the hydraulicintensifier 66 within the hydraulic brake booster 60 is inoperative; andthe vehicle braking system 18 operates as was previously described withrespect to the known vehicle braking system of FIG. 2.

In the event that the engine is turned off, or there is a failure in thevacuum system 30, or the engine is operating in a manner that there isinsufficient vacuum pressure, the pressure differential between thepressure chambers 36, 38 of the vacuum booster disappears and the vacuumbooster 26 becomes inoperative. The pressure sensor 62 within thehydraulic brake booster 60 senses an increase in pressure in the vacuumsystem 30 and switches the state of its output signal on line 63. Thesecond state of the pressure sensor output signal causes the bypassvalve 64 to switch to its second, closed state, thereby terminating thedirect fluid connection between the master cylinder 24 and the wheelcylinders 44, 46.

With the bypass valve 64 closed, pressure builds up at the inlet 92 ofthe hydraulic intensifier 60. The application of a hydraulic fluidpressure on the smaller area 89 a on the larger end 76 of the steppedpiston 75 within the O-ring 88 creates a force that is sufficient toovercome the biasing force of the spring 71. The piston 75 then movesslightly to the left as viewed in FIG. 1A, thereby creating a largerchamber or cavity 100 between the interior surface 90 of the cap 84 andthe larger end surface 89 as shown in FIG. 1B.

The formation of the inlet chamber 100 permits hydraulic fluid from themaster cylinder 24 to be applied across the entire cross-sectional areaof the larger bore 72. As will be appreciated, hydraulic fluid pressureis applied not only on the upper surface 89 of the piston 75 but also onan annular area of O-ring 80 that is between the outer circumference ofthe larger piston end 76 and the circumference of the larger bore 72.The presence of hydraulic fluid in the inlet chamber 100 results in anintensifier force being applied on the piston 75 that is equal to themathematical product of the cross-sectional area of the larger bore 72times the pressure of the hydraulic fluid at the fluid inlet 92 of thehydraulic intensifier 66. That intensifier force is mechanicallytransferred through the stepped piston 75 to the hydraulic fluid in thesmaller bore 74. The intensifier force produced by the hydraulicpressure on the larger end 76 of the piston 75 when divided by thecross-sectional area of the smaller bore 74, results in a largerhydraulic fluid pressure at the fluid output 94 of the hydraulicintensifier 66 to the wheel cylinders 44, 46.

Therefore, the hydraulic intensifier 66 effectively multiplies thepressure from the master cylinder 24 to a larger magnitude as a functionof the cross-sectional areas of the bores 72, 74 of the stepped bore 70.For example, if the cross-sectional area of the larger bore 72 is twiceas large as the cross-sectional area of the smaller bore 74, thehydraulic intensifier 66 effectively doubles the hydraulic fluidpressure received from the master cylinder 24. In the example describedpreviously, in the manual mode, that is, without the operation of thevacuum booster 26, when the operator depresses the brake pedal 20, thebraking system provides a braking force by the wheel cylinders of about1000 pounds. Thus, in the manual mode, with the operation of thehydraulic brake booster 60 doubling the available pressure applied tothe wheel cylinders, the hydraulic intensifier 66 causes the wheelcylinders 44, 46 to provide a braking force of about 2000 pounds. Itshould be noted that there are fractional or minimal losses in thehydraulic intensifier 66 due to the bias spring 71 and seal friction.

As will be appreciated, the pressure multiplier effect achieved by thehydraulic intensifier 60 is dependent on the differences in thecrosssectional areas of the larger and smaller bores 72, 74,respectively. Theoretically, to further increase the multiplier effectof the hydraulic intensifier 66, the cross-sectional area of the largerbore 72 can be further increased, or the cross-sectional area of thesmaller bore 74 can be decreased. However, when the pressuredifferential across the hydraulic intensifier is increased, the volumeof hydraulic fluid that must be supplied to the inlet chamber 100 alsoincreases. For example, if the stepped piston 75 were a straight piston,there would be no pressure differential across the piston 75; and thevolume of hydraulic fluid supplied to the inlet chamber 100 would beequal to the volume of fluid displaced from the outlet chamber 102.However, in the described example, the larger bore 72 has twice thecross-sectional area of the smaller bore 74; and therefore, twice thevolume of hydraulic fluid will be required in the inlet chamber 100 todisplace the stepped piston 75 through the outlet chamber 102 andprovide the doubled hydraulic fluid pressure at the fluid output 94. Toprovide the increased volume of hydraulic fluid to the inlet chamber 100requires more fluid from the master cylinder 24 and that, in turn,requires a greater stroke or displacement of the pushrod 22 and brakepedal 20. Thus, the pressure multiplying effect of the hydraulicintensifier 66 is limited by the available stroke of the pushrod 22 andbrake pedal 20.

The hydraulic pressure intensifier provides a vehicle braking systemhaving an improved braking capability when the braking power boost isinoperative, which may occur either when the vehicle engine is off, orthere is a failure in the power boost system or the vehicle engine isnot operating normally. Under such conditions, the hydraulic pressureintensifier provides a substantially greater braking force in responseto a force applied by an operator on a brake pedal. Thus, a vehiclebraking system with the hydraulic pressure intensifier substantiallyimproves the operator's capability of stopping the vehicle in a shortertime and over a shorter distance.

While the invention has been illustrated by a description of oneembodiment and while the embodiment has been described in considerabledetail, there is no intention to neither restrict nor in any way limitthe scope of the appended claims to such detail. Additional advantagesand modifications will readily appear to those who are skilled in theart. For example, in the described embodiment, a vacuum sensor 62 isused to determine when the engine is not operating at a level sufficientto provide the necessary vacuum pressure for power braking; and thevacuum sensor 62 is used to actuate the bypass valve 64. As will beappreciated, other bypass valve actuators may be used. For example,engine speed can be sensed, and a control signal produced when theengine speed is so low that, normally, an insufficient vacuum pressureis available for the desired power braking operation. As will beappreciated, other engine operation conditions may also be sensed inorder to provide a bypass valve actuator.

Further, referring to FIG. 1, the hydraulic brake booster 60 is shownproviding a pressure boost to the two wheel cylinders 44, 46. As will beappreciated, in another application, it may be desirable to provide apressure boost to the other two wheel cylinders 48, 50. In thatapplication, a hydraulic brake booster 60 a, which is identical instructure and operation to the hydraulic brake boost 60, is fluidlyconnected between the master cylinder 24 and wheel cylinders 48, 50.

Therefore, the invention in its broadest aspects is not limited to thespecific details shown and described. Consequently, departures may bemade from the details described herein without departing from the spiritand scope of the claims, which follow.

What is claimed is:
 1. An apparatus for use with a vehicle brakingsystem having a brake pedal adapted to be used by an operator, a pushrodhaving one end connected to the brake pedal, a master cylinder having amechanical input connected to an opposite end of the pushrod, and atleast one wheel cylinder, the braking system further including a boosterconnected to a vacuum system, the apparatus comprising: a hydraulicpressure intensifier comprising an intensifier inlet adapted to befluidly connected to an output of the master cylinder, an intensifieroutlet adapted to be fluidly connected to an input of the wheelcylinder, an intensifier cylinder having a stepped internal bore with alarger end having an interior surface receiving the intensifier inletand a smaller end adjacent the intensifier outlet, an intensifier pistonhaving a larger end disposed in the larger end of the intensifiercylinder and a smaller end disposed in the smaller end of theintensifier cylinder, the larger end having a larger end face, and aseal contacting the larger end face when the larger end face ispositioned immediately adjacent the interior surface, the seal formingan enclosed volume intersecting the intensifier inlet, the enclosedvolume being bounded by the larger end face and the interior surface ofthe intensifier cylinder and having a cross-sectional area substantiallyequal to a cross-sectional area of the smaller end of the piston, abiasing element disposed between the smaller end of the piston and thesmaller end of the cylinder for biasing the intensifier piston towardthe larger end of the cylinder, a sealing ring disposed on the smallerend of piston to fluidly separate the smaller and larger ends of theintensifier cylinder, and a vent path having one end intersecting anannular volume between the smaller end of the intensifier piston and thelarger end of the intensifier cylinder, and the vent path having anopposite end extending through a wall of the intensifier cylinder; apressure sensor connected to the vacuum system and having an outputproviding a first state in response to a normal pressure in the vacuumsystem, and a second state in response to an abnormal pressure in thevacuum system; and a bypass valve operatively connected to the pressuresensor, the bypass valve having an input fluidly connected to an outputof the master cylinder and the intensifier inlet and an output fluidlyconnected to the wheel cylinder and the intensifier outlet, the bypassvalve having an open state for fluidly connecting the master cylinder tothe wheel cylinder via the bypass valve in response to the first stateof the output of the pressure sensor, and a closed state fluidlyconnecting the hydraulic pressure intensifier between the mastercylinder and the wheel cylinder in response to the second state of theoutput of the pressure sensor, whereby a fluid pressure from the mastercylinder applied to the inlet of the intensifier cylinder is multipliedto a greater fluid pressure at the outlet of the intensifier cylinderand applied to the wheel cylinder.
 2. The apparatus of claim 1 whereinthe hydraulic pressure intensifier further comprises a sealing ringdisposed on the larger end of the intensifier piston to provide a fluidseal between the larger end of the intensifier piston and the larger endof the intensifier cylinder.
 3. A hydraulic pressure intensifiercomprising: an intensifier inlet; an intensifier outlet; an intensifiercylinder having a stepped internal bore with a larger end having aninterior surface receiving the intensifier inlet and a smaller endadjacent the intensifier outlet; an intensifier piston having a largerend disposed in the larger end of the intensifier cylinder and a smallerend disposed in the smaller end of the intensifier cylinder, the largerend having a larger end face, a seal contacting the larger end face whenthe larger end face is positioned immediately adjacent the interiorsurface, the seal forming an enclosed volume intersecting theintensifier inlet, the enclosed volume being bounded by the larger endface and the interior surface of the intensifier cylinder and having across-sectional area substantially equal to a cross-sectional area ofthe smaller end of the piston; a biasing element disposed between thesmaller end of the piston and the smaller end of the cylinder forbiasing the intensifier piston toward the larger end of the cylinder; asealing ring disposed on the smaller end of piston to fluidly separatethe smaller and larger ends of the intensifier cylinder; and a vent pathhaving one end intersecting an annular volume between the smaller end ofthe intensifier piston and the larger end of the intensifier cylinder,and the vent path having an opposite end extending through a wall of theintensifier cylinder.
 4. The apparatus of claim 3 wherein the hydraulicpressure intensifier further comprises a sealing ring disposed on thelarger end of the intensifier piston to provide a fluid seal between thelarger end of the intensifier piston and the larger end of theintensifier cylinder.